1. Field of the Invention
The present invention relates to a method of transferring a substrate or mask or mask suitable for patterning a projection beam of extreme ultraviolet electromagnetic radiation, a storage box, and an apparatus adapted for use in such a method.
2. Description of the Related Art
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning device may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged, onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once. Such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction. Since, in general, the projection system will have a magnification factor M (generally  less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be seen, for example, from U.S. Pat. No. 6,046,792.
In a known manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. It is important to ensure that the overlay (juxtaposition) of the various stacked layers is as accurate as possible. For this purpose, a small reference mark is provided at one or more positions on the wafer, thus defining the origin of a coordinate system on the wafer. Using optical and electronic devices in combination with the substrate holder positioning device (referred to hereinafter as xe2x80x9calignment systemxe2x80x9d), this mark can then be relocated each time a new layer has to be juxtaposed on an existing layer, and can be used as an alignment reference. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clens.xe2x80x9d However, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791.
Since no materials are known to date to be sufficiently transparent to EUV radiation, a lithographic projection apparatus employing EUV radiation is envisaged to employ a reflective mask having a multilayer coating of alternating layers of different materials, for instance, in the order of 50 periods of alternating layers of molybdenum and silicon or other materials, such as, for example, disclosed in European patent application EP 1 065 532 A. The size of the features to be imaged in EUV lithography makes the imaging process very sensitive to any contamination present on the mask. It is foreseen that any contaminant particles having a dimension in the order of 50 nm will result in defects present in devices fabricated in the substrate. Conventionally, the patterned side of the reticle is covered by a pellicle. Any contamination will then accumulate on the pellicle surface at some distance from the mask pattern and will therefore not be (sharply) imaged onto the substrate, making such masks having pellicles less sensitive to contamination. Pellicles cannot be employed for EUV radiation since they will not be sufficiently transparent to EUV radiation. Particle contamination on the pattern-bearing reflective surface of the mask would therefore lead to defective devices fabricated and must be prevented.
Further, the reflective mask is envisaged to be held at its backside on the mask table by electrostatic forces on a mask-bearing surface to be able to meet the very stringent requirements for EUV mask positioning. Any contaminant particles present in between the backside of the mask and the mask-bearing surface of the mask table will result in irregularities of the reflective mask surface. Since the projection system will be non-telecentric on the object side because a reflective mask is used (more information on this problem can be derived from European patent application EP 1 139 176 A), any irregularity in the surface figure of the reflective mask surface will translate into a local shift of the pattern imaged onto the substrate. As a result, the imaged layer may not line up with earlier layers that have been processed in the substrate, again leading to defective devices being fabricated. Therefore, particle contamination on the backside surface of the mask must be prevented.
Molecular type of contamination, such as hydrocarbons and water, should also be prevented. Such contamination will have a detrimental effect on any optical components in the lithographic apparatus, including the mask. In all handling procedures of masks and substrates, care should be taken that their surfaces will remain clean from such molecular contamination.
Masks and substrates may be stored and transported in between various types of apparatus employing a storage box in which a protective environment is maintained, such as an environment that is evacuated or filled with an inert gas. Inside walls of such a storage box should also remain clean. However, while transferring a mask or substrate out of such a storage box to an apparatus for processing or employing such substrate or mask, contamination, both particulate contamination and molecular contamination may be introduced onto the mask or substrate or internal walls of the protective environment. It is possible to transfer a mask or substrate through some intermediate chamber, for instance, a load lock chamber, to a final environment for processing or use, but then it may require very long times before such contamination is removed from the intermediate chamber, for instance, very long pump down times when the protective environment is to be evacuated.
It is an aspect of the present invention to provide a transferring method in which the introduction of contamination into a protective environment is largely reduced or even fully prevented.
This and other aspects are achieved according to the invention in a method for transferring one or more substrates or masks in a storage box to an apparatus for handling, processing or using the substrates or masks, the storage box including a cover having an openable cover part, the method including providing the storage box onto an openable wall part of a wall of an enclosed protective environment of the apparatus such that the openable cover part overlaps the openable wall part, the protective environment being adapted to be filled with an inert gas or to be evacuated; opening the openable cover part and the openable wall part, whereby the cover forms part of the wall and an inside of the storage box becomes part of the protective environment; and transferring at least one of the substrates or masks from an inside space of the storage box to an inside space of the protective environment, or vice versa.
According to further aspects of the present invention there are provided a storage box and an apparatus for use in the above method.
According to yet a further aspect of the present invention there is provided a device manufacturing method including providing a substrate that is at least partially covered by a layer of radiation-sensitive material; providing a projection beam of extreme ultraviolet radiation using a radiation system; using a reflective mask to endow the projection beam with a pattern in its cross-section so as to provide a patterned beam of radiation; projecting the patterned beam of radiation onto a target portion of the layer of radiation-sensitive material; and transferring one or more masks or substrates according to the above method.
Although specific reference may be made in this text to the use of the apparatus according to the present invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. One of ordinary skill will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget portionxe2x80x9d, respectively.
In the present document, the terms xe2x80x9cradiationxe2x80x9d and xe2x80x9cbeamxe2x80x9d are used to encompass extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range 5-20 nm).